The present invention relates to low oil pressure switches which shut off an engine when the oil pressure is below a predetermined level. More particularly, the invention relates to an interlock switch for disabling the low oil pressure switch to permit the engine to be easily started.
Various types of low oil pressure switches are known which activate when the engine oil pressure is below a predetermined level. Some of these prior art switches are connected to indicator systems that provide an audible or visual signal when the oil pressure is too low.
When other types of oil pressure switches activate, they cause the engine to shut off to prevent engine damage. One such oil pressure switch is connected in series with the primary winding of the ignition system's main core, and is normally open. This type of switch closes when the oil pressure is below a predetermined level, thereby grounding the ignition pulse and stopping the engine.
Another type of oil pressure switch is normally closed when the engine is running. The switch then opens when the oil pressure is below a predetermined level, causing the engine to shut down.
A major problem with both of the above-referenced shut-off switches is that the engine is thereafter difficult to start. Since the engine has been shut off due to low oil pressure, it is very difficult to generate a sufficient oil pressure by pulling or cranking the engine to then cause the oil pressure switch to deactivate. Moreover, such low oil pressure shut-off switches typically activate while the engine is being shut off for any reason since the sensed oil pressure is low as the engine is winding down. In addition, the operator may not know why the ne will not start, and may attempt to find other possible problems with the engine which prevent it from starting.
It is thus desirable to provide a means for starting an engine which has been shut down, and at the same time to indicate to the operator that the oil pressure is low.